Method and apparatus for providing welding power

ABSTRACT

A method and apparatus for providing welding type power is disclosed. A welding type power supply includes an input circuit, a controller and an output circuit. The input circuit receives an input power signal and provides an intermediate power signal. The output circuit receives the intermediate power signal and provides a welding type power output. The output circuit has an inverter with at least two inverter switches, and a clamp circuit that limits the voltage across the inverter. The clamp circuit captures and buffers the excess energy, and returns the excess energy to an input of the inverter over a plurality of switching cycles. The controller has control outputs connected to the input circuit and the output circuit, to control them.

RELATED APPLICATIONS

This is a divisional of, and claims the benefit of the filing date ofU.S. patent application Ser. No. 13/843,926, filed on Mar. 15, 2013,which issued on Feb. 19, 2019 as U.S. patent Ser. No. 10/207,351.

FIELD OF THE INVENTION

The present disclosure relates generally to the art of providing weldingtype power. More specifically, it relates to providing welding typepower using an inverter based output circuit.

BACKGROUND OF THE INVENTION

There are many known types of welding-type power supplies that providewelding type power. Welding type power, as used herein, refers to powersuitable for electric arc welding, plasma are cutting or inductionheating. Welding-type power supply, as used herein, refers to a powersupply that can provide welding type power. Welding type systems areused to perform a variety of processes and used in a variety ofsettings. Welding-type system, as used herein, is a system that canprovide welding type power, and can include control and power circuitry,wire feeders, and ancillary equipment.

Some welding type systems include a preregulator which provides a dcbus, followed by an inverter based output circuit. The preregulatorconditions the input power, and provides a known dc bus. The inverterbased output circuit receives the bus and provides the welding typepower as an output. One successful design includes a boost circuit aspart of the preregulator, and the output circuit includes an inverter,transformer, rectifier and output inductor. This type of welding typepower supply is described in U.S. Pat. No. 6,987,242 (Geissler). Otherwelding type power supplies that have inverter based output circuitsinclude U.S. Pat. No. 6,115,273 (Geissler) and Patent Publication20090230941 (Vogel), all three of which are owned by the owner of thispatent, and all three of which are hereby incorporated by reference.Other welding type power supplies include additional stages, or useother topologies for each stage (such as a buck preregulator, a combinedrectifier-boost preregulator, a chopper instead of or following theinverter, a second inverter following the first inverter, etc.

Inverter based output circuits offer many advantages, but they do havesome drawbacks. First, the switches and diodes used in an invertercircuit can fail, particularly when exposed to higher than ratedvoltages. Clamping voltages is known, but can result in excess losses.Also, commutating switches and diodes can create excess heat. U.S. Pat.No. 6,801,443 returned the entire clamp energy back into the output inone single switching event.

Most welding type power supplies include and output inductor. Startingthe welding process can be difficult, particularly with a large outputinductor, because the inductor must be “charged” before welding can bepreformed. This can be made more difficult during starting because ofthe higher than usual arc voltage. Past welding type power supplies havestarted by a “crowbar” of the bus but that can stress components.

Accordingly, a welding type power supply with an inverter output circuitthat is clamped in an efficient manner is desirable. Preferably, suchwelding type power supply would also provide for efficient commutationsof devices and will provide for efficient starting of the weld process.

SUMMARY OF THE PRESENT INVENTION

According to a first aspect of the disclosure a welding type powersupply includes an input circuit, a controller and an output circuit.The input circuit receives an input power signal and provides anintermediate power signal. The output circuit receives the intermediatepower signal and provides a welding type power output. The outputcircuit has an inverter with at least two inverter switches, and a clampcircuit that limits the voltage across the inverter. The clamp circuitcaptures and buffers the excess energy, and returns the excess energy toan input of the inverter over a plurality of switching cycles. Thecontroller has control outputs connected to the input circuit and theoutput circuit, to control them.

According to a second aspect of the disclosure a method of providingwelding power includes receiving input power and providing anintermediate power signal. The intermediate power signal is inverted bycontrolling at least two inverter switches to provide an inverteroutput. The voltage across the inverter is clamped and the excess energyis captured and buffered provided to an input of the inverter over aplurality of switching cycles.

The clamp circuit includes a buck circuit in one embodiment.

The output circuit includes an intermediate inverter, a transformer anda rectifier in another embodiment. The intermediate inverter receivesthe intermediate power signal and provides an intermediate ac signal tothe transformer. The transformer provides a transformed ac signal to therectifier. The rectifier provides a rectified dc signal to the inverter.

The rectifier includes at least two diodes and a second clamp circuitlimits the voltage across the at least two diodes, and provides anoutput across the voltage source in another embodiment.

The clamp circuit includes a voltage source connected to the buckcircuit in one alternative.

The inverter is a half bridge inverter with two inverter switches or ais a full bridge inverter with four inverter switches in otheralternatives.

The buck circuit has a buck switch, and feedback indicative of thevoltage across the clamp is provided to the controller so that thecontroller controls the buck switch in response to the voltage acrossthe inverter in yet another embodiment.

According to a third aspect of the disclosure a welding type powersupply includes an input circuit, an intermediate inverter, atransformer, a rectifier an output inductor and a controller. The inputcircuit receives an input power signal and provide an intermediate powersignal. The intermediate inverter receives the intermediate power signaland provides an intermediate ac signal. The transformer receives theintermediate ac signal and provides a transformed ac signal. Therectifier receives the intermediate ac signal and provides a rectifieddc signal to the inductor. The rectifier includes at least two diodesand a clamp circuit that limits the voltage across diodes and capturesthe excess energy. The controller controls the input circuit and theintermediate inverter.

According to a fourth aspect of the disclosure a welding type powersupply includes an input circuit, an output circuit, and a controller.The output circuit receives the intermediate signal and provides awelding-type signal. The output circuit includes an output inductor andan inverter. The inverter has at least two inverter switches. Theinverter includes a clamp circuit having a voltage source and the clampcircuit is connected to charge the inductor. The controller controls theinput circuit and the output circuit.

The clamp circuit limits the voltage across the inverter, and includes abuck circuit that can be used to assist in arc striking and stabilizing

The output circuit includes a transformer and a rectifier having atleast two diodes, and a second clamp circuit limits the voltage acrossthe at least two diodes and provides an output across the voltage sourcein another embodiment.

The input circuit includes a boost circuit, and the intermediate powersignal is a boosted dc bus in another embodiment.

Other principal features and advantages will become apparent to thoseskilled in the art upon review of the following drawings, the detaileddescription and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a welding-type system in accordance with thepreferred embodiment;

FIG. 2 is a full bridge inverter circuit used as an intermediateinverter;

FIG. 3 is a clamp circuit for an inverter;

FIG. 4 is a clamp circuit for an inverter;

FIG. 5 is a diagram of an output circuit; and

FIG. 6 is a full bridge inverter circuit used as an output inverter.

Before explaining at least one embodiment in detail it is to beunderstood that the invention is not limited in its application to thedetails of construction and the arrangement of the components set forthin the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting. Like referencenumerals are used to indicate like components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present disclosure will be illustrated with reference to aparticular circuit and a particular system, it should be understood atthe outset that other circuits and systems may be used.

Generally, the preferred embodiment is implemented with a welding-typesystem such as that shown in U.S. Pat. No. 6,987,242. It includes apreregulator input circuit that creates an intermediate power signal(preferably a dc bus), an output circuit with an inverter, atransformer, and a rectifier and a controller. Additionally, an outputinverter is provided in the preferred embodiment, for ac welding. Theoutput inverter receives the transformed and rectified signal, andprovides an ac welding signal. An output inductor is provided,preferably after the inverter. Alternatives provide for the inductorbeing before the output inverter, omitting the output inverter, using achopper, using a buck preregulator, using a combined boost-rectifierpreregulator, omitting the boost (and inverting the rectified input).

Input circuit, as used herein, includes the circuitry that receivesinput power such as rectifiers, filters, preregulators, etc.Intermediate power signal, as used herein, includes the output of theinput circuit, and can be a rectified signal, a regulated signal such asthe output of a boost or buck converter, or an unregulated dc bus.Output circuit, as used herein, includes the circuitry that provides thewelding type signal, and can include inverters, converters,transformers, rectifiers, filters, chokes, etc. Controller, as usedherein, is the digital and/or analog circuitry and/or logic/instructionsthat cooperate to provide control signals to one or more circuits. Acontroller can be located on a single board, or distributed acrossmultiple locations.

The preferred embodiment has a clamp circuit for the output inverter,and a clamp circuit for the output rectifiers. The clamp circuit for theoutput inverter includes a buck converter which takes the energy fromclamping and gradually recycles the excess energy back into the outputcircuit (to the input of the output inverter) and maintains a controlledstable clamp voltage. The buck circuit also clamps the output rectifierdiodes and assisting in arc striking and stabilizing by applying thehigh clamp voltage to the output to counter the high arc voltagetransient that are encountered. In other word, the output of the clampcircuit for the output diodes is fed back to the output inverter clampto act as a voltage source. Also, the 300 volt source can be used toquickly charge the output inductor.

Clamp circuit, as used herein, refers to a circuit used to clamp thevoltage across circuitry to protect that circuitry, such as clamping thevoltage across a diode. Clamp circuit output, as used herein, refers tothe energy that is clamped being provided to other circuitry.

FIG. 1 is a diagram of a welding-type system 100 in accordance with thepreferred embodiment. Welding-type system 100 includes an input circuitor preregulator 102, an output circuit 104 and a controller 106. Thesemodules are preferably designed as shown in U.S. Pat. No. 6,987,242,except as set forth herein.

Preregulator 102 is preferably a boost preregulator, but othertopologies such as buck, cuk, etc. may be used. Preregulator 102preferably provides a 940V regulated dc bus across a capacitor 103 toinverter 104. Other embodiments provide for an unregulated bus, or foradditional stages as part of input circuit 102, between input circuit102 and output circuit 104, or before or as part of output circuit 104.

Output circuit 104, shown in more detail in FIG. 5, preferably includesa full bridge inverter 501, a transformer 503, an output rectifier 504,a full bridge output inverter 507 and an output inductor 509. Inverters501 and 507 each include at least four inverter switches. Inverter 501receives the dc, bus and inverts it to a desired signal using PWM at afrequency of about 20 KHz-40 KHz. The frequency is preferably highenough to keep transformer 503 small. The load is a primary oftransformer 503, and the secondary of transformer 503 is rectified to bea welding type output. Output inverter 507 inverts the welding typeoutput to provide an ac welding output. If dc welding is provided outputinverter 507 can be turned off (or omitted for only dc welding powersupplies). Output inverter 507 preferably operates a welding processfrequency of about 20-400 Hz. Alternatives provide that on or both ofinverters 501 and 504 be half bridges, or that other topologies areused. A half bridge inverter includes at least two inverter switches.Inverter switch, as used herein, refers to a switch used to invert asignal. A single inverter switch maybe comprised of several paralleldevices that function as a single switch.

Controller 106 may be discrete components or an integrated circuit, andit may be analog or may include a combination of analog and digitalcontrol elements, Controller 106 receives the necessary feedback frompreregulator 102 and output circuit 104 to control the switches in thosecircuits such that the desired dc bus and the desired welding typeoutput are provided.

FIG. 2 shows a typical full bridge inverter circuit with four inverterswitches S1-S4, and four diodes D1-D4, and capacitors C1 and C2. Theload is the primary of transformer T1. The secondary of transformer T1is rectified and provided as the welding-type output.

Output circuit 104 also includes a clamp circuit as part of inverter 507to limit the voltage across inverter 507. A clamp circuit 300 is shownin FIG. 3 and includes a buck inductor 302, a buck switch 304, diodes306 and 308, capacitor 310 and voltage source 312. The output of clampcircuit 300 is provided to the input of inverter 507 (the output ofrectifier 505). Thus, the energy from clamping is recovered and used inthe welding output. As described below, the 300 volt source can berecovered from clamping output diodes, it can be a separate source, or acombination of independent voltage and recovered voltage.

The buck converter is also used to assist in arc striking andstabilizing. The weld control can override the regular buck convertercontrol (returning energy to the weld) and have it apply the higherclamp voltage to the input of the inverter or the rectified dc link.This allows a high driving voltage to be applied to the output whenneeded. Limiting the voltage across the inverter, as used herein, refersto clamping the voltage across the diodes in an inverter bridge. Voltageacross the inverter, as used herein, refers to the voltage across thediodes in an inverter bridge

Buck switch 304 is controlled to provide three advantages in thepreferred embodiment. Current (from the output rectifier clamp) isrecycled back to the input of output inverter 507 in a gradualcontinuous fashion (i.e., over a plurality of switching cycles), andthus the clamped energy is provided back into the weld output in agradual fashion, and it keeps the clamped voltage under control. Also,buck switch 304 is controlled to aid in reversing the current duringcommutation of the switches in output inverter 507 by providing a highvoltage to the output circuit to counter the transient high arc voltageand keep the current in the output inductor rising. Also, buck switch304 is controlled to provide a high voltage to counter the high initialarc voltage and help the current start to rise at the initiation of theweld. The 300 volt source can be used to commutate at low current output(when there is neither a need to clamp not sufficient energy fromclamping to commutate). Buck switch 304 is controlled by controller 106,which receives feedback signals indicating bus, clamp and invertervoltages. 300 volt source 312 is also used in the preferred embodimentto charge output inductor 509 rather than crowbarring the bus.

Output circuit 104 includes the secondary of primary 503, rectifier 505,including diodes 402 and 404, as shown in FIG. 4. A diode 406 clampsdiodes 402 and 404, and that clamp is provided as a voltage source 412.This voltage can override the 300 volt source, or the 300 volt sourcecan be derived from source 412. FIG. 6 shows output inverter 507 in moredetail, which includes switches 601-604. Capacitor 310, diode 306 andoutput inductor 509 are also shown.

Alternatives include clamping only output inverter 507 or only outputdiodes 402 and 404, not providing the 300V source, as well as not usingthe clamped voltage to commutate inverter 507, or not using the 300Vsource to charge output inductor 509.

Numerous modifications may be made to the present disclosure which stillfall within the intended scope hereof. Thus, it should be apparent thatthere has been provided a method and apparatus for providing weldingtype power that fully satisfies the objectives and advantages set forthabove. Although the disclosure has been described specific embodimentsthereof, it is evident that many alternatives, modifications andvariations will be apparent to those skilled in the art. Accordingly,the invention is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

The invention claimed is:
 1. A method of providing welding power,comprising: receiving an input power signal and providing anintermediate power signal; converting the intermediate power signal to awelding type signal, including inverting a dc signal by controlling atleast two inverter switches in a cyclical fashion to provide an inverteroutput, and clamping the voltage across the inverter and capturing andbuffering the excess energy, and returning the excess energy from agiven cycle to the inverter over a plurality of subsequent switchingcycles; and a controller having control outputs connected to the inputcircuit and the output circuit.
 2. The method of claim 1, whereinclamping further includes controlling a buck circuit.
 3. The method ofclaim 2, wherein clamping further includes providing a voltage source tothe buck circuit.
 4. The method of claim 1, wherein inverting includesat least one of half-bridge inverting and full bridge inverting.
 5. Amethod of providing welding power, comprising: receiving an input powersignal and providing an in mediate power signal; converting theintermediate power signal to a welding type signal, including invertinga dc signal by controlling at least two inverter switches to provide aninverter output, wherein converting further includes receiving andinverting the intermediate power signal to provide an intermediate acsignal, transforming the intermediate ac signal into a second ac signal,rectifying the second ac signal to provide the dc signal; and clampingthe voltage across the inverter and capturing and buffering the excessenergy, and returning the excess energy to the inverter over a pluralityof switching cycles; and a controller having control outputs connectedto the input circuit and the output circuit.
 6. The method of claim 5,further comprising, clamping the rectified output with a clamp circuithaving an output, and providing the output of the clamp circuit as thevoltage source.